Sometimes I forget I’m an electrical engineer. I was working in the basement, trying to clean the place up a bit, when I took a long look at the old Ampeg M-12A Mercury (7591 tubes, not the older version — probably an early 1964 model) guitar amp. That damn thing always shocked the Hell out of me every time I used it, but it sounds really good with the Rickenbacker model 1997 reissue. I have a copy of the schematics, so I took a look and came to the conclusion that I’m lucky to be alive…. That floating ground is an accident waiting to happen. That all has to go! So I made a slight modification (changed out the plug so the bad boy is properly grounded) and everything is perfect. Except that the tremelo is broken because the caps are dried up. Everything about this amp is original …. from the Jensen speaker to all the tubes. And it still works and it sounds great.
Modified Schematic:
Original Schematic section:
Having a problem finding theree .05uf 400v capacitors (Tiny Chief) that will (probably and hopefully) repair the vibrato function on the amplifier. As far as I know this has never worked, so those caps have probably been bad for a long time. If it’s not those three capacitors, then there must be a broken connection or some other capacitor that is causing a problem.
Comment by Mick — — 26-July-2005 @ 17:10 UTC